I recently put my Koodo phone on suspend for two months for a trip to the US.

I recently put my cell phone on suspend for two months for a trip to the US. I want to reactivate it but my old plan is not available. If I chose a different plan, will I be stuck with it for two years?

That's right you have to pick a current plan each time. It's often not worth it to do it for that reason if you have a good grandfathered plan. But there's no requirement to keep any plan you pick. Your only restriction will be one change per billing cycle.